class Phone:
    """
    This class represents a phone.
    """
    IMEI = None  # International Mobile Equipment Identity
    SIM_ID = None  # Subscriber Identity Module
    ICCID = None  # Integrated Circuit Card Identifier
    MSISDN = None  # Mobile Subscriber International ISDN Number
    producer = None

    def call_by_4g(self):
        print("4g通话")
